12.5.6. Drought

In the Australia and New Zealand region, droughts are closely related to major
drivers of year-to-year and decadal variability such as ENSO, Indian Ocean SSTs,
the Antarctic Circumpolar Wave (White and Peterson, 1996; Cai et al.,
1999; White and Cherry, 1999), and the Interdecadal Pacific Oscillation (Mantua
et al., 1997; Power et al., 1998; Salinger and Mullan, 1999), as well
as more or less chaotic synoptic events. These are all likely to be affected
by climate change (see Sections 12.1.5 and 12.2.3,
and TAR WGI Chapters 9 and 10).

Using a transient simulation with the NCAR CCMO GCM at coarse resolution (R15)
(Meehl and Washington, 1996), Kothavala (1999) found for northeastern and southeastern
Australia that the Palmer Drought Severity Index indicated longer and more severe
droughts in the transient simulation at about 2xCO2 conditions than
in the control simulation. This is consistent with a more El Niño-like
average climate in the enhanced greenhouse simulation; it contrasts with a more
ambivalent result by Whetton et al. (1993), who used results from several
slab-ocean GCMs and a simple soil water balance model. Similar but less extreme
results were found by Walsh et al. (2000) for estimates of meteorological
drought in Queensland, based on simulations with the CSIRO RCM at 60-km resolution,
nested in the CSIRO Mk2 GCM.

A global study by Arnell (1999), using results from an ensemble of four enhanced
greenhouse simulations with the HadCM2 GCM and one with HadCM3, show marked
decreases in runoff over most of mainland Australia, including a range of decreases
in runoff in the Murray-Darling basin in the southeast by the 2050s of about
12-35%. HadCM3 results show large decreases in maximum and minimum monthly
runoff. This implies large increases in drought frequency.

The decrease in rainfall predicted for the east of New Zealand by downscaling
from coupled AOGCM runs for 2080 and the corresponding increase in temperature
are likely to lead to more drought in eastern regions, from East Cape down to
Southern Canterbury. Eastern droughts also could be favored by any move of the
tropical Pacific into a more El Niño-like mean state (see Table
3-10). The sensitivity of New Zealand agriculture and the economy to drought
events was illustrated by the 1997-1998 El Niño drought, which was
estimated to result in a loss of NZ$618 million (0.9%) in GDP that year. A drought
in north and central Otago and dry conditions in Southland associated with the
1998-1999 La Niña resulted in a loss of about NZ$539 million in
GDP (MAF, 2000).

Recurring interest in Australia in policies on drought and disaster relief
is evidence of a problem in managing existing climate variability and attempts
to adapt (O'Meagher et al., 1998). Present variability causes fluctuations
in Australian GDP on the order of 1-2% (White, 2000). Drought and disaster
relief helps immediate victims and their survival as producers (e.g., QDPI,
1996) but does not reduce costs to the whole community and in fact may prolong
unsuitable or maladapted practices (Smith et al., 1992; Daly, 1994),
especially if there is climatic change. Farm productivity models are being used
to simulate past and present farm production and to assess causes of and management
options for coping with drought (Donnelly et al., 1998). This is contributing
to the fashioning of drought assistance and advisory policies.

The potential impact of drought on the Australian economy has declined, in
relative economic terms, over time in parallel with the decline in the importance
of agriculture to the economy (ABARE, 1997; Wilson and Johnson, 1997). In 1950-1951,
the farm sector constituted 26.1% of GDP, whereas currently (1997-1998)
it constitutes 2.5%. Similarly, the contribution of the farm sector to Australian
exports has fallen from 85.3% (1950-1951) to 19.6% (1997-1998), with
a reduction in the total farm sector labor force of about 6%. This despite the
fact that farm production has increased over the same period. Thus, drought
remains an important issue throughout Australia for social, political, geographical,
and environmental reasons (Gibbs and Maher, 1967; West and Smith, 1996; Flood
and Peacock, 1999).

Stehlik et al. (1999) studied the impact of the 1990 drought on more
than 100 individuals from 56 properties in central Queensland and northern NSW
to document the social experiences of dealing with drought. They conclude that
there is strong evidence that the impact of the extended drought of the 1990s
is such that rural Australia will never be the same again: "There is a
decline in population: a closing down of small businesses, fewer and fewer opportunities
for casual or itinerant work, more and more producers working off-farm'
and a reduction in available services."

A change in climate toward drier conditions as a result of lower rainfall and
higher evaporative demand would trigger more frequent or longer drought declarations
under current Australian drought policy schemes, which rely on historical climate
data and/or land-use practices on the basis of an expectation of historical
climatic variability. A major issue for operational drought schemes is the choice
of the most relevant historical period for the relative assessment of current
conditions (Donnelly et al., 1998).

Examples of Australian government involvement in rural industries that have
been subject to decline in commodity prices over several decades (e.g., wool)
suggest that the industries will be supported until the cost to the overall
community is too high and the long duration or high frequency of drought declarations
is perceived as evidence that the drought policy is no longer appropriate (Mercer,
1991; Daly, 1994). In the case of wool, the shift of government policy from
that of support to facilitation of restructuring has involved a judgment about
future demand and therefore prices (McLachlan et al., 1999) and has only
occurred after an extended period of low prices (Johnston et al., 1999).
With a change in climate toward drier conditions, drought policy probably would
follow a similar path.

The New Zealand Government response to drought comes under Adverse Climatic
Events and Natural Disasters Relief policy that was released in 1995. Government
responds only when rare climatic or natural disasters occur on a scale that
will seriously impact the national or regional economy and the scale of the
response required is beyond the capacity of local resources. The policy is to
encourage industry/community/ individual response, rather than reliance on government
support.

Science has a major role in assessing the probability that recent and current
climatic conditions could be the result of natural variability or increased
GHGs. At best, these assessments are presented in probabilistic terms (e.g.,
Trenberth and Hoar, 1997). The public and its representatives will have to judge
what constitutes evidence of anthropogenic effects and to what extent future
projections and their impacts should be acted on. Because of their impact, future
droughts provide a very public focus for assessing the issues of climate change
compared to natural variability. Appropriate land-use and management practices
can be reassessed by using agricultural system models with CO2 and
climate projections from GCMs (Hall et al., 1998; Howden et al.,
1999f; Johnston et al., 1999). However, political judgments between the
alternatives of supporting existing land use or facilitating reconstruction
are likely to require greater certainty with regard to the accuracy of GCMs
than is currently available (Henderson-Sellers, 1993).

12.5.7. Pests and Diseases

Cropping, horticulture, and forestry in Australia and New Zealand are vulnerable
to invasion by new pests and pathogens for which there are no local biological
controls (Sutherst et al., 1996; Ministry for the Environment, 1997).
The likelihood that such pests and pathogensparticularly those of tropical
or semi-tropical originwill become established, once introduced to New
Zealand, may increase with climate warming.

Indepth case studies are being conducted in Australia to test the performance
of pest impact assessment methodologies for estimating the vulnerability of
local rural industries to pests under climate change (Sutherst et al.,
1996). In New Zealand, pests that already are present may extend their ranges
and cause more severe damage. For example, because of the reduced incidence
of frosts in the north of New Zealand in recent years, the tropical grass webworm
(Herpetogramma licarisalis) has increased in numbers and caused severe
damage in some pastures in the far north.

The vulnerability of horticultural industries in Australia to the Queensland
fruit fly Bactrocera (Dacus) tryoni under climate change was examined
by Sutherst et al. (2000). Vulnerability was defined in terms of sensitivity
and adaptation options. Regional estimates of fruit fly density, derived with
the CLIMEX model, were fed into an economic model that took account of the costs
of damage, management, regulation, and research. Sensitivity analyses were used
to estimate potential future costs under climate change by recalculating costs
with increases in temperature of 0.5, 1.0, and 2°C, assuming that the fruit
fly will occur only in horticulture where there is sufficient rainfall or irrigation
to allow the crop to grow. The most affected areas were the high-altitude apple-growing
areas of southern Queensland and NSW and orange-growing areas in the Murrumbidgee
Irrigation Area. Apples and pears in southern and central NSW also were affected.
A belt from southern NSW across northern Victoria and into South Australia appeared
to be the most vulnerable.

Adaptation options were investigated by considering, first, their sustainability
under present conditions and, second, their robustness under climate variability
and climate change. Bait spraying is ranked as the most sustainable, robust,
and hence most promising adaptation option in boh the endemic and fruit fly
exclusion zones, but it causes some public concern. The sterile insect technique
is particularly safe, but there were concerns about costs, particularly with
large infestations. Exclusion is a highly effective approach for minimizing
the number of outbreaks of Queensland fruit fly in fly-free areas, although
it is vulnerable to political pressure in relation to tourism. These three techniques
have been given the highest priority.